1. Field of the Invention
The present invention relates to the technical field of digital signal processing and, more particularly, to a recursive type-IV discrete cosine transform (DCT) system.
2. Description of Related Art
With the development of digital signal processing technologies, various messages and media information can be conveniently obtained in daily living. A variety of modified discrete cosine transforms (MDCTs) and inverse modified discrete cosine transforms (IMDCTs) are widely used in various audio codec standards.
The audio codec standards include MP3, AAC, AC-3, TwinVQ, Ogg, for example. The MDCT and IMDCT operations in an audio codec occupy a very large portion of the entire operational complexity. If the MDCT/IMDCT is implemented with a same approach, sharing the hardware can be achieved on design for reducing the hardware requirement and the MDCT/IMDCT operational complexity.
For a high-efficiency Advanced Audio Coding (HE-AAC) audio codec, it uses high-quality spectral band replication (HQ-SBR) or low-power spectral band replication (LP-SBR) technologies in which complex-domain analysis quadrature mirror filter-banks (complex AQMFs) and synthesis quadrature mirror filter-banks (complex SQMFs) can be derived as the DCT of type III (DCT-III) and DCT-II kernel methods. Therefore, for implementing an aspect of AQMF and SQMF co-architecture in design, in addition to the MDCT and IMDCT computation, the operation of DCT-IV/DCT-III/DCT-II supports is accounted an essential key in hardware design.
However, the typical recursive architecture for IMDCT implementations has the disadvantages of having numerous operational periods and the overtime computation and being difficult to implement a co-architecture design for different operations such as the MDCT, AQMF at a decoder and the SQMF at an encoder. When the typical recursive architecture requires increasing the bit rate, only the hardware or the timing can be increased. However, the increased hardware indicates to increase the cost, and the increased timing indicates the high power consumption. In addition, for concurrently having the MDCT, AQMF, SQMF operational capabilities, it needs to design different hardware architectures for the operations, which also indicates the additional cost for hardware design.
Although the recursive discrete Fourier transforms (RDFTs) have developed for many years and thus advanced, it is still required for further reducing the operational complexity and hardware cost and increasing the data computational performance.
Therefore, it is desirable to provide an improved RDFT system to mitigate and/or obviate the aforementioned problems.